The invention relates to a device for joining a panel and any structure, between which significant forces are to be transmitted.
The invention applies in particular to the case where the panel is made of a composite material and where the structure is made of metal. However, it is not restricted to this particular case and also relates, for example, to the assembly of a metal panel and a metal structure.
The joint device according to the invention may particularly be used in aeronautics, for example in order to provide the connection between the wing and the fuselage of an aircraft, between wing panels and between fuselage sections. The joint device according to the invention may also be used in the space field, for example to assemble different sections of a launcher or of its boosters. Indeed, it allows the condition of the panel surfaces and, consequently the aerodynamic properties of the assembly not to be too markedly affected.
A usual technique of joining two parts consists in using at least one joint plate. This is placed on the parts to be assembled and connected to each of them by mounting components such as rivets, bolts etc. This assembly technique is particularly used in aeronautics, for example to make the joints between the wing and the fuselage of an aircraft. It may also be used to make the joints between two parts of the wing or between two parts of the fuselage.
However, this known technique is long and tricky to implement, particularly since it requires great precision of the bores, into which the mount components are received. Moreover, the excess thickness due to the presence of the joint plate may, in certain cases, pose problems of assembly (for example during the assembly of two elements of a thin wing: the small distance between the lower surface and the upper surface then makes it difficult to install a joint plate through the inside of the wing), or of aerodynamics (for example in the case of a joint plate mounted on the outer surface of a wing).
A known technique for joining two parts without creating a disturbance relative to the aerodynamics consists in using a connection known as a xe2x80x9cpianoxe2x80x9d, by virtue of its appearance, which is reminiscent in design of the keys of a piano. In this type of assembly, adjacent cut-outs or recesses are machined on the outer surfaces of the metal panels, along the edges to be assembled. Assembly is provided by bolts orientated along a direction approximately perpendicular to the joint surface of the panels and approximately parallel to their outer surface. Each bolt includes a nut and a head received respectively in two cut-outs facing each other of the assembled panels. If necessary, the continuity of the machined surface of the panels is provided by covering the channels with a protective plate or by filling them with a resin (for example when the assembly is made on an outer surface of the aeroplane; surface continuity then allows aerodynamic problems to be reduced).
However this assembly technique may be difficult to apply when one of the panels is made of a composite material. Indeed, machining deep juxtaposed cut-outs near the panel edge would make the latter lose a major part of its mechanical strength in this area.
Document U.S. Pat. No. 5,171,099 describes a device allowing a composite material panel and another structure to be assembled together. This device includes a set of mounts, evenly distributed along the interface between the parts.
Each mount includes a first hole, pierced in the composite material panel, perpendicular to its surfaces and near the edge to be assembled. A hollow cylinder, in which is housed a nut called a xe2x80x9cbarrel nutxe2x80x9d, captive in said cylinder, is inserted into this first hole. A second hole, approximately parallel to the panel surfaces, passes through the latter between the edge to be assembled and the first hole, approximately equidistant from said surfaces, in other words near the neutral fibre of the panel.
In this known arrangement, the assembly of the two parts is provided, in each mount, by a tension screw, which passes through the second hole formed in the panel as well as a flange integral with the structure onto which it is desired to fix the panel. More exactly, the head of the screw is supported on the flange while its threaded end is screwed into the barrel nut.
Such a device makes it possible to solve the problem posed by joining a composite material panel and another structure. However, it does not make it possible to transmit between the two parts all the forces which the structural elements could withstand if they were not weakened by the device, as shown in FIG. 1 of the appended drawings.
FIG. 1 shows an orthonormal frame in which has been shown as x-coordinates the pitch P (expressed, for example, in mm) separating two consecutive mounts of the joint device described in the document U.S. Pat. No. 5,171,099 and as y-coordinates the flux F transmitted between the two parts, in other words the force transmitted per unit of length of the joint. The flux F may particularly be expressed as daN/mm.
As is shown by curve A in FIG. 1, the flux F which may be withstood by the tension screws of the different mounts (assuming screws of constant section) increases when the number of mounts made on an joint device of given length increases, in other words when the pitch P separating two consecutive mounts diminishes.
Curve B in FIG. 1 shows the tear flux of the joint device, in other words the flux for which the composite material panel tears along the line formed by the first holes, under the effect of the forces applied between the two parts. Curve B shows that the maximum flux able to be transmitted through the joint device diminishes when the pitch P separating two consecutive mounts diminishes. Indeed, the closer the holes housing the barrel nuts are to each other, the less material there is between the latter in the composite material panel. This leads to an embrittlement of the panel, which may then tear approximately along the line formed by the holes.
The maximum flux, which may therefore be transmitted through the joint device under consideration, corresponds to the flux F0 given by the intersection of curves A and B in FIG. 1. It is obtained for a pitch P0 between the mounts.
Consequently, the joint device described in the document U.S. Pat. No. 5,171,099 is not adapted when the forces, which have to be able to be transmitted through it, exceed the maximum flux F0, as is the case in certain applications, particularly in aeronautics.
The exact object of the invention is an joint device using mounts comparable to those which are described in the document U.S. Pat. No. 5,171,099, in order particularly to be able to provide the joint between a composite material panel and another structure, while having an original arrangement allowing appreciably greater forces to be transmitted.
According to the invention, this outcome is obtained by means of a device for joining a panel and another structure, this device including a plurality of mounts distributed along an interface between the panel and the structure, each of the mounts including a nut embedded in the panel, near the interface, and a tension screw passing through parts of the panel and the structure adjacent to the interface, along a direction approximately perpendicular to the interface, said screw including a head supported on the structure and a threaded end screwed into the nut, characterised in that the nuts of the different mounts are arranged along at least two rows approximately parallel to the interface, in such a way that the nuts of the adjacent mounts are located in different rows.
As will be seen in greater detail subsequently, for a given number of mounts, of identical dimensions, this arrangement makes it possible to increase, in the panel, the quantity of material between two adjacent nuts and, consequently, to increase the flux of forces able to be transmitted by the joint device.
In a preferred embodiment of the invention, each nut is mounted in a cylinder which passes through the panel along a second direction approximately perpendicular to the first direction and to the surfaces of said panel.
To advantage, each cylinder then includes a countersunk head, housed in a complementary cavity formed on an outer surface of the panel, in such a way that an end surface of said head is flush with said outer surface. This arrangement makes it possible particularly to preserve the aerodynamic properties of the panel, in aerospace applications.
In this case, each cylinder also includes, preferably, a threaded end onto which is screwed a second nut supported on an inner surface of the panel. This arrangement is particularly advantageous in the event of the panel being made of composite material. Indeed it makes it possible to reduce the phenomena of delamination of this material, which could be caused by applying tensile/compressive forces essentially through the cylinders in which the nuts are mounted.
According to a first embodiment variant of the invention, the tension screws of the mounts of which the nuts are arranged in different rows transmit appreciably different forces and have larger cross-sections when the forces transmitted are more significant.
According to a second embodiment variant of the invention, the tension screws of the mounts of which the nuts are arranged in different rows transmit appreciably different forces and are made of a material having greater tensile strength when the forces transmitted are more significant.
According to a third embodiment variant of the invention, the tension screws of the mounts of which the nuts are arranged in different rows transmit appreciably different forces and clamp more tightly when the forces transmitted are smaller.
A preferred application of the invention relates to the case where the panel is made of a composite material. This application must not however be considered as restricting the scope of the invention, since the latter also relates to the assembly of metal panels.
Lastly, when the structure with which the panel is assembled is a metal panel, recesses used to house the heads of the tension screws are to advantage of machined into this metal panel.